Aging of the immune system is associated with reduction of immunologic competence in man and experimental animals. However, with advancing age there is also an increased prevalence of autoimmune diseases and serum autoantibodies in the elderly. It is not known whether the age-associated autoantibodies arise primarily by the process of somatic mutation, arise from the germ line genes or are due to appearance of cross-reactive antibodies, all in concert with a reduction in overall immunity. Age-associated autoantibodies are generally of the IgM class and studies from this laboratory have identified the bone marrow in the elderly human as playing a role in their development. How major a role needs to be determined. The currently proposed experiments will attempt to determine the celluar origin of age-associated bone marrow autoantibodies, the age-related changes in their regulation, and their relationship to autoantibodies associated with autoimmune diseases, taking IgM anti-IgG (rheumatoid factor, RF) and IgM anti-human thyroglobulin (IgM anti-Tg) as representatives. We will conduct investigations using counter flow centrifugal elutriation for cell separation; phenotypic analyses with monoclonal antibodies, fluorescence activated cell sorter analysis, and idiotypic antibody analyses for characterization; human B cell-B cell hybridization and in vitro autoantibody induction assays to elucidate the nature of the autoantibody secreting population. Anti-idiotypic antibody immunoblotting analysis of serum and human hybridization autoantibody molecules fractionated by polyacrylamide gel electrophoresis and by isoelectric focusing gels will be used to study their heterogeneity and biochemical properties. Analysis of human bone marrow B cell-B cell hybridomas secreting RF autoantibodies by Southern blotting, amino acid sequencing, and nucleic acid sequencing techniques will be used to elucidate the molecular heterogeneity of the age-associated autoantibodies. It is anticipated that the combination of a cellular and molecular approach will elucidate the origin of age-associated autoantibodies and identify the immunologic dysfunctions which contribute to the development of autoantibodies and autoimmunity in the elderly human.